Phantom limb pain relieved when amputated arm is put back to work

​Max Ortiz Catalan has developed a new method for the treatment of phantom limb pain (PLP) after an amputation. The method is based on a unique combination of several technologies, and has been initially tested on a patient who has suffered from severe phantom limb pain for 48 years. A case study shows a drastic reduction of pain.

​People who lose an arm or a leg often experience phantom sensations, as if the missing limb were still there. Seventy per cent of amputees experience pain in the amputated limb despite that it no longer exists. Phantom limb pain can be a serious chronic and deteriorating condition that reduces the quality of the person´s life considerably. The exact cause of phantom limb pain and other phantom sensations is yet unknown.

Phantom limb pain is currently treated with several different methods. Examples include mirror therapy (see fact box), different types of medication, acupuncture and hypnosis. In many cases, however, nothing helps. This was the case for the patient that Chalmers researcher Max Ortiz Catalan selected for a case study of the new treatment method he has envisaged as a potential solution.

The patient lost his arm 48 years ago, and had since that time suffered from phantom pain varying from moderate to unbearable. He was never entirely free of pain.The patient´s pain was drastically reduced after a period of treatment with the new method (see image). He now has periods where he is entirely free of pain, and he is no longer awakened by intense periods of pain at night like he was previously.

The new method uses muscle signals from the patient´s arm stump to drive a system known asaugmented reality. The electrical signals in the muscles are sensed by electrodes on the skin. The signals are then translated into arm movements by complex algorithms. The patient can see himself on a screen with a superimposed virtual arm, which is controlled using his own neural command in real time.

”There are several features of this system which combined might be the cause of pain relief” says Max Ortiz Catalan. “The motor areas in the brain needed for movement of the amputated arm are reactivated, and the patient obtains visual feedback that tricks the brain into believing there is an arm executing such motor commands. He experiences himself as a whole, with the amputated arm back in place.”

Modern therapies that use conventional mirrors or virtual reality are based on visual feedback via the opposite arm or leg (see fact box). For this reason, people who have lost both arms or both legs cannot be helped using these methods.

”Our method differs from previous treatment because the control signals are retrieved from the arm stump, and thus the affected arm is in charge” says Max Ortiz Catalan. ”The promotion of motor execution and the vivid sensation of completion provided by augmented reality may be the reason for the patient improvement, while mirror therapy and medicaments did not help previously.”

A clinical study will now be conducted of the new treatment, which has been developed in a collaboration between Chalmers University of Technology, Sahlgrenska University Hospital, the University of Gothenburg and Integrum. Three Swedish hospitals and other European clinics will cooperate during the study which will target patients with conditions resembling the one in the case study – that is, people who suffer from phantom pain and who have not responded to other currently available treatments.

The research group has also developed a system that can be used at home. Patients will be able to apply this therapy on their own, once it has been approved. An extension of the treatment is that it can be used by other patient groups that need to rehabilitate their mobility, such as stroke victims or some patients with spinal cord injuries.

In addition to pain relief, the treatment also resulted in several other effects that are positive for the patient:

He now experiences that his phantom hand has a position of rest as its normal state. He previously felt like it was a permanently and strongly closed fist. This might be linked to the pain relief since it arose at the same time.

He has learned to control the movements of his phantom hand, even when he is not connected to the treatment system. He has gradually improved in this respect. Now he can go as far as to move each individual finger.

He has restored a perception effect that often arises after amputations – that the phantom hand is perceived as being located directly on the stump – so that he now experiences the phantom hand as being at the anatomically correct location.

These results show how complex our body perception is. It can change based on feedback from our senses, and by the brain´s motor commands being expressed through muscle contractions.

More about: How the new method works

The treatment is based on a combination of different technologies developed by the research group:

Patterns of myoelectric signals are converted to movement in a virtual arm. Part of the arm must remain in order for signals to be produced, and the more muscles that remain, the more movements can be created.

An environment for augmented reality where the patient can see him or herself with the virtual arm. Augmented reality means that the perception of the physical world is extended by means of virtual reality.

Computer games that promotes motor execution in a fun and gratifying manner.

Max Ortiz Catalan has published the motion prediction technology as open source, Biopatrec, so that researchers all over the world can explore, apply, and extend it.

More about: Advantages of the method

Provides a whole, in which all of the parts correlate in a natural manner. The patient´s desire to use the amputated arm activates the appropriate area of the brain and generates real signals in the amputated arm´s nerves and muscles, and augmentation leads to realistic visual feedback.

Is not invasive (does not require surgery).

Can be used when both arms (or legs) have been amputated.

Enables most of the movements that a biological arm can execute.

Generates motivation with computer games, and exact measurements of the patient´s progress.

More about: Mirror therapy and virtual reality

Mirror therapy for phantom pain was introduced in the 1990s. It is based on tricking the brain into believing a missing arm or leg still exists by using visual feedback to the brain. The amputee executes movements with his or her healthy arm or leg, and at the same time attempts to execute the same movements with the missing limb. A large mirror reflects the healthy side´s movements, which gives the patient a visual illusion that both arms or legs are functioning normally.

Therapy with virtual reality is a modernization of this concept. Instead of using a mirror, the patient sees a virtual arm or leg. Today´s treatments are still based on the movements of the healthy arm or leg.

Both treatment methods only work on certain amputee patients.

More about: The research

Max Ortiz Catalan is a PhD student at Chalmers University of Technology and Sahlgrenska University Hospital. The new treatment method has been developed as a side project to his primary research area on neural control of limb prostheses.

Professor Bo Håkansson at Chalmers University of Technology, and Associate Professor Rickard Brånemark at Sahlgrenska University Hospital and the University of Gothenburg, are his PhD supervisors. Two Master of Science thesis projects, by Nichlas Sander and Morten Kristoffersen, have contributed to the augmented and virtual reality environments. The research is funded by Jimmy Dahlstens Fond, Conacyt, Vinnova, Picosolve, IKV, and Integrum.